


nyahllergies

by osakiss



Category: IDOLiSH7 (Video Game)
Genre: "sickfic" theyre both just catboys, Cat Ears, Catboy Condition, Gentle Kissing, Grinding, Implied Relationships, M/M, Sibling Bonding, Sibling Incest, Sickfic, but cos it was barely even mentioned i didnt tag it, dk how but they are, it gets a little spicy, izumicest is in this too, riku gets a pinch in, slight nipple play
Language: English
Status: Completed
Published: 2020-10-04
Updated: 2020-10-04
Packaged: 2021-03-06 17:48:53
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,630
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26312914
Author URL: https://archiveofourown.org/users/osakiss/pseuds/osakiss
Summary: Riku caught a case of the catboy, and his dear Tenn-nii comes to his rescue.
Relationships: Kujou Ten/Nanase Riku
Comments: 9
Kudos: 33





	nyahllergies

**Author's Note:**

  * For [Idekbuthi](https://archiveofourown.org/users/Idekbuthi/gifts).



> hhshjfhksf!!!!!! happy!!!! birthday fariye!!!!!!!!! ilove you so much have catboy tennriku ilyilyily

The moment Tenn disconnected the call he rushed to gather his mask and other materials for going outside. Riku getting sick wasn’t a big deal, not really, since it was such a frequent endeavor. But this time… this time something was off. Iori of all members called him, and seemed panicked at that. Iori was surely used to him being sick by now, so this had Tenn quite worried. 

“Where are you heading off to?” Gaku asked, seeing Tenn rushing to put on his coat.

Tenn opened the door and replied with a single word. “Riku.” He placed his mask on and left the room. Gaku just sighed, hoping Tenn would remember to text him what exactly happened when he wasn’t fretting over his brother again. Tenn wasn’t wasting any time getting into the car, demanding for the driver to fast as possible towards where Idolish7 resided. 

The driver didn’t take his time, noting that Tenn seemed to be stressed about reaching there as fast as possible. Once the car pulled up in front of the establishment, Tenn rushed to the car door and ran out. He came back and apologized, before thanking the driver for taking him here. The driver nodded and Tenn took that as his cue to book it towards Riku. He was growing more worried over his brother as time went on. What could possibly be wrong with him now?

Tenn has dealt with several different types of sick Rikus in his childhood. Due to his asthma, his entire respiratory system was weakened which made him more susceptible to disease. He knew exactly how to soothe Riku no matter his condition. Was this a condition he hasn’t seen before? And Iori got to see it first… he didn’t know to feel about that. That someone else knew what he knew regarding how to care for Riku. He still believed he knew better than that pompous high-schooler though. Tenn pressed the buzzer and waited for someone to see him.

Inside, Mitsuki went to see who was at the door. He was met with Tenn’s face twisting in pure concern for Riku’s wellbeing. Mitsuki quickly allowed him in, and ushered him towards Riku’s room.

“Iori won’t let anyone see what’s wrong with him, so I’m not sure what’s going on. You’re his brother, so maybe this is something you’ve dealt with before?” Mitsuki sighed. “Anyway, hopefully it’s nothing too bad. Iori sounded really panicked, but that just might be because he didn’t know what to do.” Tenn thanked Mitsuki for all the information given to him and bowed politely. Mitsuki laughed and left him to enter Riku’s room alone. Tenn breathed in and out before knocking on the door gently.

Iori opened the door and upon recognition let Tenn into the room where Riku was kept. Tenn scanned the room for his precious twin, who he found to be in his bed and in a blanket burrito. There wasn’t any sign of Riku being sick. His face wasn’t flushed pink, he wasn’t breathing irregularly, no sweat, nor any look of pain in his eyes. He seemed fine, exceptionally better then when he actually was sick.

So, what could possibly be wrong with him?

“Nanase-san. Please, show Kujou-san your head.” His… head? If he was called over here due to some swelling, he might just strangle Iori, Riku’s feelings regarding that be damned.

Riku sighed and reluctantly removed the blanket from his head to reveal large cat ears. The blanket was draped over his shoulders, and his face was a hue of pink now, but clearly different from when he was sick. Tenn’s darling brother was embarrassed. He was embarrassed of showing Tenn, but not Iori? He didn’t know whether to be angry at Iori or happy that Riku was blushing. Riku’s blush was extremely adorable, after all. His lips were pursed and he was looking to the side, his long lashes making it look like he was batting his eyes when he was blinking quickly. He was nervous for Tenn’s response. 

“Sorry for bothering you, Tenn-nii.” Riku looked to the side, his lips forming a pout. Iori looked at Tenn worriedly.

“Do you have any idea how to help him?” His voice shook with desperation. “We can’t go on without Nanase-san on stage with us. His voice is the heart of Idolish7, and we can’t let him be seen like this. I’m not even sure if it’s an illness or something else. I’ve never seen or heard anything like this.” Tenn nodded. He forgot to get mad at Riku for letting this affect his job as an idol, thank god for Iori reminding him. 

However, Tenn had never dealt with something like this before. What even was this? How does someone suddenly sprout cat ears? He’d need to discuss with Riku in great detail regarding what happened before this change. It could lead to clues regarding how which would then help to reverse it as well. 

Tenn nodded. “I can figure out a way to solve this. Give me two days. You’ll need to leave.” Iori bit his lip in frustration. He wanted to be there with Riku, to nurse him back to health himself, but agreed to his conditions nonetheless and left the room, leaving the two brothers alone. If it was for the betterment of Idolish7, he would just have to suck it up.

Riku shifted closer to Tenn once Iori shut the door. “Tenn-nii, are you sure about this? You could get sick too.” He pouted, still blushing. Tenn wanted nothing more than to kiss him right then and there. Or maybe pat his head? Riku did have cat ears… and he loved cats. Tenn adored Riku, and Tenn adored cats. This was a combo-attack on his heart.

He gave into his urges and stroked Riku’s head. The boy mewled and nuzzled into his brother’s hand. So cute. “We don’t know what this even is. Doesn’t seem like a disease either. I have a plan to get to the bottom of it, don’t worry.” Riku beamed. 

"Does that mean we have the whole day to ourselves, Tenn-nii?” Riku’s smile was dazzling. It was so bright, Tenn could feel all his worries evaporate. A complete sunshine, his precious baby brother was.

Tenn nodded instead of replying, and continued to stroke his brother’s head. Riku got more comfortable and eventually left his burrito, which revealed another feature that Iori neglected to mention.

Riku laid his head down on Tenn’s thighs, the stroking not stopping. He curled around his brother’s backside, nuzzling his brother’s lap. Tenn heard something swishing in the air, but ignored it in favor of petting Riku. He seemed to enjoy it a lot after all.

Tenn felt something smack his back and he looked back only to see a tail. A tail? Tenn followed to where the tail came from and low and behold it’s from his newly-catboy twin brother.

“You have a tail too, Riku?” Riku sat up, effectively cutting off the petting. He missed Riku’s soft locks already. But the look on Riku’s face was worth it.

His lips were parted, embarrassed and clearly wanting to say something but unable to let anything out. The blush had spread across his entire face and to his ears as well, he was burning up. Riku was blinking rapidly, looking around the room and gesticulating in an attempt to explain but with no voice to back him up. Tenn chuckled into his fist and continued to pet his head. Riku settled down to that and crawled back into Tenn’s lap. Good, it’s where he belongs.

“You’ll have to answer some questions in order for you to turn back, Riku. Can you answer them?” Tenn asked gently. Riku nodded fervently, to which Tenn chuckled again. His enthusiastic brother truly was the cutest. Such an obedient puppy. Riku’s tail wrapped around Tenn.

“Alright. What’s the last thing you remember before you became a catboy?”

Riku pursed his lips while trying to recall. Once again, Tenn was hit with the urge to kiss his brother. One arm crossed over the other and holding it, the other hand raised up so that his fingertips touched his lips. Riku snapped his fingers and stared at his brother.

“I remember waking up like this, but you mean what I did before I slept, right?” Tenn nods and lets Riku continue. 

“Well, I was thinking of someone I really love,” His baby brother likes someone? Tenn knew it would happen someday. The day Riku went off and married someone that wasn’t him. Most people don’t love their brothers in the way he loves Riku, after all. Doesn’t do anything to soothe the ache in his heart though. Tenn bit the inside of his lip, making sure not to show his grief on his face. Last thing he needed was to worry Riku.

“And I realized that that person could never possibly return my feelings. It’s a lost cause. Honestly, I still think he hates me sometimes, and it hurts.” Tenn wanted to click his tongue so bad. How dare someone not be in love with Riku? Riku was the best thing since sliced bread. Actually, even better than sliced bread. His own heart may shatter and break, but as long as Riku keeps sharing his radiant smile with the world then Tenn will suffer happily.

Tenn looks into Riku’s eyes and caresses his cheek.

“He would be a fool not to love you. Aside from that, I think I know the root of the problem.” Riku blushed. He couldn’t help but to flush in his Tenn-nii’s presence. His heart fluttered whenever he glanced at him, and couldn’t control the pace of how fast it was beating whenever Tenn touched him.

“Yeah?” Riku leaned into the touch, “What is it, Tenn-nii?” Riku’s eyes fluttered shut as he rubbed his cheek against Tenn’s hand. Tenn didn’t know what to do. Kiss Riku? But he loved someone else. He wanted to kiss Riku’s cheeks so badly. So adorable, so completely precious. He could feel his heart thudding in his chest and he had to control his facial expression so it didn’t show how completely and utterly head over heels he was for Riku. _Control yourself, Kujo Tenn!_

“Most likely from perceived unreciprocated love. All you need to do is confess to the one you love and have them confess back and you should return to normal. Even if they don’t reciprocate, it could possibly be keeping the feelings without revealing them. Confessing should easily cure you of this.” 

Riku looks in awe. “You’re so smart, Tenn-nii!” He hooks his arms around Tenn’s neck and pulls him in for a quick hug. Tenn’s face started to burn up. Such close proximity… he didn’t know what to do with him. His brother’s affection for him was going to get him into trouble. 

“Well, it’s only a theory. We should test it out.” Riku stiffened. “So, Riku? Do you want me to call in Iori now or later?” Tenn’s heart shattered into several different pieces as he uttered the words. No way he lost to the brat high-schooler, right? But then again, they had more time to bond from being in the same group plus they’re not related in any way. It’d made sense for Riku to like him. 

Tenn wanted so desperately for Riku to love him back. Immoral or not, he didn’t care for that. He only cared for Riku. The entire reason he became an idol was for his sake, after all. Riku’s smile was all that mattered. No matter if Tenn thought he was the best pick, or that only he had the right to wed Riku. It didn’t matter, Riku’s choice did. He’ll respect it, no matter how much it kills him to.

Riku only tilted his head in confusion.

“Why would you call Iori?”

“To confess.” Tenn stared into his brother’s eyes. He so badly wanted to avert his gaze, but it was important to see the reaction that’d get from. Riku made a grimace and shook his head.

“Bzzt! You’re wrong!” Riku backed up and made an X shape with his arm, sticking his tongue out. Tenn raised an eyebrow at that, and kept back a smirk. Suck it, high-schooler. But that raised another question. 

“Who is it then, Riku?” He shuffled closer to Riku, very little space between them. Riku’s face was the same color as his hair. Riku shook his head.

“I can’t tell you that.” Riku averted his gaze.

“Why not? In order to figure out if this works, you’ll need to confess.”

Riku shook his head. “Can we please talk about it tomorrow? You said we have two days, so we can use them up.” 

Tenn’s expression grew serious. “Riku, this isn’t just about you. Your group is depending on you, and your fans are all eagerly awaiting to see you. You’re an idol, act like it. Don’t disappoint them.” Riku shook his head even more.

“I know that! And I want to go on stage and perform for them! I want to make them smile! But I can’t. If I confess, it will permanently ruin everything.” Riku clutched his chest, the panic making him breathe more heavily. Tenn held Riku’s hand and quietly sang in his ear as he once did.

Tenn will let it go for today. He could pressure Riku as much as possible the next day. For today, he’ll comfort his brother. 

They stayed like that for a while. Tenn gently held Riku’s hand as he gripped back. His breathing had returned to normal long ago, so there was no longer any reason for the two to hold hands like this. The two fell into easy conversation. They talked about their daily lives, schedules, and members. Tenn felt at ease. Learning about the Riku he dearly loves makes him happy.

Tenn always regrets not being able to see Riku grow up. He wanted to see what kind of friends Riku made, what he had trouble with in school, what he loved to do. In some ways, Riku was a complete stranger. But that wasn’t true, they had such a sweet history together. 

Their moment was interrupted by a knock. Tenn got up and peaked to see who it was. Iori, of course.

“Have you made any progress?” Iori asks. Tenn nods, filling him in on his hypothesis. 

“Please get him to confess by tomorrow.” Tenn almost clicked his tongue. He didn't need this brat to tell him what to do.

“Will do.” Tenn turned but he tried to shut the door, Iori popped back in. He just couldn’t get rid of this kid.

“Would you like dinner? It is quite late.” Tenn turned to Riku, who quickly nodded. Iori bowed and took his leave to retrieve them dinner. Because of that Tenn realized he never told Gaku anything and pulled out his phone. 

_To: trigger's menace_

_Hey, I’m fine. Riku got a strange sickness, so Iori called me. I’ll be back the day after tomorrow’s morning._

Satisfied, Tenn put his phone back in his pocket and went over to his younger brother. He truly was grateful that they were on break, or else he didn’t know what he would do with him. Riku’s ears twitched and his tail waved in the air, side to side. Tenn smiled gently and scratched the back of Riku’s ear, earning him a mewl from his brother.

“Tenn-nii, that feels really good!” Riku took Tenn’s free hand and held it tightly. His smile was infectious. A knock at the door interrupted them. Tenn wanted to click his tongue and ban Iori from entering so they could continue, but he had their dinner.

Iori placed the tray on the table beside them and bowed, wishing them a good night and exiting the room. They whispered their thanks and quickly finished their food, leaving the dirty dishes in the tray to put away in the morning. Riku scratched his cheek and gave Tenn a nervous smile. 

“Do you wanna sleep with me? Just like how we used to?” The question was so innocent but Tenn blushed. Being in close proximity with Riku drives him crazy, but he couldn’t refuse him. Tenn nods instead of verbally responding, but Riku’s eyes shone all the same.

Riku rocked forward. “Really? Thank you, Tenn-nii!” The younger twin got up and grabbed some sleepwear and handed a pair to Tenn. “I’ll change in the corner, so you can change over there.” Tenn couldn’t stop sneaking glancing at Riku’s naked body from the corner, staring at his ass. They finished up and placed their daytime clothing elsewhere, and got into bed.

Tenn laid down on the bed first, patting his stomach to Riku with a gentle smile adorning his face. Riku quickly climbed onto the bed and placed his head onto Tenn’s stomach, the relief and nostalgia flooding his veins. 

“Goodnight, Tenn-nii.” Riku closed his eyes, and smiled at Tenn’s “Goodnight, Riku.”

Tenn waited until he felt his brother’s breathing even out, signaling he was knocked out cold.

His shoulders relaxed and he pressed a kiss into Riku’s hair. His hair was so soft, he wanted to lay in it forever. Tenn pressed his nose back into Riku’s hair and nuzzled him, though careful not to wake up. 

He couldn’t resist the urge to press a few more kisses on his brother’s head. He even tried the daring move of kissing Riku’s new cat ears, despite knowing they were sensitive and Riku might awake. Riku only rustled a little on his stomach, but didn’t wake. Tenn hugged Riku by the shoulder and rested his cheek back atop Riku’s head, inhaling his scent. Tenn wanted to enjoy every moment of this, while Riku was asleep—

A thought made him freeze. Whoever it is Riku likes, they surely like him back. Riku will be able to do all these things with someone else. Cuddling, kissing, small gestures of affection. Everything Tenn ever wanted with his dear brother. He couldn’t ever dare do these things with Riku awake, but that person would. That person would be able to do everything and more to Riku, and Tenn would be forced to deal with it for the sake of his twin’s happiness.

Tenn could feel his heart resume the crumbling process. He wanted to cry, but had long lost the ability to do so. With that sullen mood, he fell into slumber.

* * *

When Tenn opened his eyes, he was greeted with the sight of Riku’s lips on his. The younger twin was grinding down on Tenn’s groin, his arms behind Tenn’s neck. Riku broke their kiss and stared at his older brother with a smirk.

“Good morning, Tenn-nii.” Riku greeted him, his eyes staring at him with a lust he’s never seen before.

“Riku, what are you doing?” Tenn asked, breathless. He could feel himself getting hard at Riku’s constant grinding, which was going to be a problem.

“A problem?” Oops, he said that out loud.

Riku only winked. “That’s okay, Tenn-nii. I’ll gladly help you with that.” Tenn blushed. What had gotten into Riku? There was no way. This was going too fast for him, but everything felt so good he supposed they could leave the feelings discussion for later. Riku continued grinding, his breathing hitching. 

“Tenn-nii, I think I’m close. I want to cum.” He looked over to Tenn with hazy eyes. “But I want you to cum first.” Tenn was sure that his boner just grew in size to those words alone.

Riku slowly crawled down to Tenn’s pants and began to unbuckle. 

“Tenn-nii.”

Tenn shivered at his brother’s voice.

“Tenn-nii!”

He might cum untouched if Riku kept that up.

_“Tenn-nii!!”_

Tenn jerks awake and has Riku pressed up against his face. He really hopes he doesn’t have morning wood, that would probably hurt Riku. His twin looked worried and was grabbing at something on his head. Wait— something on his head?

“Tenn-nii! You have cat ears too!” Riku whispered.

Tenn shook his head and placed his head into his palm. Of course he did. Was this something due to his Nanase blood? Unrequited love turns you into a catboy. How bizarre. 

But there were more important matters at hand. Tenn needed to confirm that Riku wasn’t aware of his wet dream, especially that the wet dream was regarding him. “Riku, did I wake you up? Or do anything weird in my sleep?”

Riku blushed and looked to the side. Shit. “You were moaning a little bit in your sleep. It’s okay if you have those kinds of dreams Tenn-nii, you don’t need to be embarrassed. We’re men, after all.” He says that, but he’s embarrassed just by the discussion of it. Riku is averting his gaze and playing with his fingers which was a dead giveaway to how he actually felt.

“Ah, I see. Sorry, Riku.” Tenn apologized. At the very least Riku didn’t know it was about him. Riku waved his arms frantically. 

“No, no! It’s fine, Tenn-nii!” He put his arms down. “Let’s go change now. Iori should be here any minute expecting a progress report from you, and to pick up the dishes, so I’ll ask him to clear out the bathrooms for us to shower.” Riku met Tenn’s gaze. “Do you want to go first or should I?”

Color blossomed all over Tenn’s face at the implication. 

“It’s fine for you to go first, Riku.”

Iori popped his head into the room without a knock this time and raised an eyebrow at their position. Riku never did get any further from his face, his hand still cradling Tenn’s ear. Riku smiled and pulled away from Tenn to ask Iori the bathroom favor.

After reporting to Iori, and promising him the problem would be solved soon and that no, catboy is not contagious, the pair left to take their morning showers. Tenn did not take a cold shower, thank you very much. He knew how to kill his boner without touching himself. After all, he wouldn’t be able to survive around Riku if he couldn’t.

They returned to the room and had their breakfasts. The rest of their day was spent watching shows, Iori visiting the two of them sometimes. They would have some idle chatter, though not discussing Tenn’s ears. They were extremely sensitive, and despite Riku knowing that he wouldn’t stop groping them throughout the day. He had to keep thinking of Gaku’s father in a speedo to will his boner down. Though, his tail was wagging constantly, especially when Riku started his little groping sessions. Riku must’ve been doing this on purpose, trying to get some kind of reaction from his brother.

However, Riku looked uneasy throughout the day, but Tenn thought Riku would bring it up eventually so he left it alone. He was right— of course he was, he knew Riku the best— and Riku opened his mouth to start speaking.

“I kept quiet about it but… you told me the reason for these ears are unrequited love, right? So, who do you love, Tenn-nii? You need to confess just as much as I do.”

The dreaded question that Tenn didn’t want to answer. No matter how much he loved Riku, there was surely no way his brother saw him in the same light. So, Tenn shook his head.

“Tenn-nii, you’re so unfair! You were yelling at me yesterday about how selfish I’m being but now you-” Tenn was no longer looking at Riku. He was right, he had no right to pressure Riku when he himself couldn’t confess. Though, it was different considering that Riku’s person was someone he actually could confess to. Riku stopped yelling the second he saw the look on his older brother’s face.

“Ah. You’re in the same position, huh? Someone we can’t confess to?” Riku smiled wide, his eyes becoming crescents. “That makes it easier! I’ll confess first,” Riku opened his eyes to stare into Tenn’s. “Then you, okay Tenn-nii?” Tenn’s eyes widened in surprise, but he couldn’t exactly back out now. Riku confessing means he can call that person and they can cure Riku. The whole reason he came here after all. It would destroy his relationship with Riku, but that’s nothing he hasn’t done before.

Tenn nods at Riku’s proposal and prepares himself for the heartbreak in Riku’s next words. His brother smiled gently and approached Tenn.

“Here I go.” Riku said, his voice barely above a whisper. Riku tenderly caressed Tenn’s cheek, getting even closer to him, his eyelids heavy.

“I love you, Tenn-nii. I always have.” 

Riku closed the gap between them, gently pressing his lips onto his brother’s. Tenn registered Riku’s lips before his confession and kissed back, moving his lips with Riku’s in a desperate manner. As if to make up for lost time. Tenn hooked his arms around Riku’s neck and pushed harder into Riku’s lips. 

They broke apart. “I love you too, Riku. There was never a moment where I didn’t.” Tenn looked into Riku’s red eyes. His heart was warm. Relief, love, and lust all flooded him at once. Riku smiled and kissed his brother again, more aggressively. He pushed Tenn down onto the bed, his tongue swirling in the older twin’s mouth. Riku reached for Tenn’s ears and began to rub the back of it. Tenn broke off the kiss and moaned obscenely before covering his mouth.

“Riku! So you did know what you were- Ah!” Another moan broke out from Tenn’s mouth. Riku used his other hand to pull up Tenn’s shirt. 

“I’ve never done anything like this before, Tenn-nii. Have you?” Riku asked, admiring Tenn’s stomach. 

“Not with anyone.” Riku hummed happily at that.

“You’re the only one I’ve ever wanted.”

Tenn smiled. “What have you imagined with me?”

“Lots of lewd things.”

Riku had uncovered Tenn’s nipples and dived down onto his brother’s chest. Tenn let out a slight gasp, still stimulated from the groping of his ear. Riku took one nipple in his hand, and licked the other one. Tenn shivered, his back arching slightly. 

Right as Riku is about to take Tenn’s nipple into his mouth, Iori enters the room.

“Nanase-san, would you like dinner-” Iori paused and took the scene before him. Riku’s face turned red and the twins scrambled out of their provocative position, Tenn shoving his shirt down with a pout. _Stupid High-school cockblock._

“I promise we can explain!” Riku’s hands were waving all over the place. His face blended well with his hair at that moment. Iori walked over to Riku’s bed and began to poke at Tenn’s body.

“Nanase-san, you should aim for here,” Tenn’s collarbone. “Here,” Tenn’s thigh. “And here.” Tenn’s sensitive nipple. “Though you should experiment with Kujou-san to see which spots he likes most.”

Riku looked at the younger incredulously. “How do you know any of that, Iori?”

Iori mouthed a name and suddenly it was clear why the two being brothers and close to fucking didn’t bother him in the slightest. The advice, while unwanted, was stored into Riku’s memory.

The night ended peacefully with Riku and Tenn cuddling in their sleep, their tails intertwining. Though, when they awoke they found that both their tails and cat ears had disappeared. Riku was disappointed, but wouldn’t voice it. He loved Tenn-nii’s mewls, after all.

Their three days were up, but the twins had already made plans during breakfast on how to arrange time for one another. Talking casually with Riku always eased Tenn. After they bid their farewells, making sure to sneak in a goodbye kiss, Tenn texted Gaku.

  
  


_To: trigger’s menace_

_Everything is alright now. More than alright._

  
  
  


_From: trigger’s menace_

_you hooked up with your brother didn’t you_

**Author's Note:**

> in case youre wondering:  
> ryuu is "trigger's playboy" while tenn is "trigger's demon"


End file.
